This invention relates to a document illumination system and more particularly to a pair of reflector elements placed on opposite sides of an optical slit so as to direct illumination towards an object point.
Prior art illumination system for line-by-line scanning of a document have provided a plurality of lamp and reflector combinations. The simplest arrangement consists of an elongated lamp located so as to direct the light emanating through an aperture onto a scan strip. The addition of reflectors either behind, or partially enveloping the lamp to increase illumination of the scanning area is also well known.
Various prior art systems have added further refinements such as introducing a second lamp/reflector combination to the other sides of a scan strip. A typical such system is disclosed in U.S. Pat. No. 3,844,653. Alternate versions omit the second lamp but maintain various reflector arrangements on the side of the exposure zone opposite the lamp, e.g. U.S. Pat. No. 3,982,116 and U.S. Pat. No. Re. 29,017.
There are many applications where it is most desirable to obtain a narrow intense illumination band at the illumination plane so as to obtain a narrow well defined exposure at the image plane. Typical of said systems are those wherein documents are imaged onto photosensor arrays or those wherein a linear lens array such as a gradient index SELFOC lens is utilized as the imaging means. Some of the above described illumination arrangements have been utilized in these systems but an optimum arrangement would include an apertured lamp on one side of the scan strip and a reflector on the opposite side of the exposure zone, the reflector configured and positioned relative to the illumination source so as to maximize illumination at the scan area of an object plane. Two low cost, efficient, illumination systems having these characteristics are disclosed in U.S. Pat. Nos. 4,118,119 and 4,190,355, both assigned to the same assignee as the present invention. With both of these systems, however, there still exists the further potential for increasing illumination efficiency by capturing an additional component of the light emanating from the illumination source aperture.
According to the present invention, an apertured light source is located adjacent an object plane to be scanned, a first reflector is located on the opposite side of the scan strip and a second reflector is placed on the same side of the exposure zone as the illumination source and between the source and the object plane. These reflectors effectively capture all of the solid angle of light subtended from the illumination source. In a first embodiment, the reflectors are of the facetted type and are arranged in a platenless continuous velocity transit (CVT) system. In a second embodiment, the reflectors are used in an arrangement wherein the document to be copied is supported on a platen and the two reflectors are modified to effectively extend into the cross-sectional area of the platen.